Recent trends show a dramatic increase in the applications of optical fiber and optical components. These new applications have placed demands not only on the optical components and their performance, but also on the packaging of these components. Today's optical packages need to be robust and suitable for a wide range of environments. Of particular interest herein are optical packages for use in high-moisture applications such as those found outdoors, in industrial plants and machinery rooms, underground or underwater.
One approach for packaging an optical component, such as a channel splitter, involves placing the component in a tube and then sealing the tube on each end with an end cap. More specifically, with reference to FIG. 1, this package 10 is assembled by applying adhesive to the perimeter of the end cap 14 (typically while rotating using a hand-operated fixture) and to the orifice in the end cap through which the fiber 15 (or wire) passes. As used herein, the term “adhesive” refers broadly to both adhesives and sealants. Next, the end cap is pushed into the tube 12. Typically, both end caps are pushed into place simultaneously. The adhesive 13 is then cured while the tube is laying on its side.
This packaging configuration is advantageous in that the end cap 14 is exposed to ambient conditions rather than the adhesive 13. Minimizing the adhesives' exposure to the environment is important since it is typically through the adhesive that moisture enters the housing and damages the optical component.
Despite the advantageous of this approach, the applicants have identified a number of problems with it. First, as shown in FIG. 1, since the epoxy 13 is typically cured while the tube 12 is on its side, an asymmetric distribution of adhesive results. This is especially problematic since it is difficult to control the application of adhesive around the perimeter of the end cap 14 in the first place, thus, often too much adhesive is applied. If too much adhesive is applied, it may interfere with the delicate internal optical component 11, especially given the asymmetric distribution of adhesive. Furthermore, the volume of adhesive may be so large that it imposes expansion/contraction stresses on the packaging during thermal cycling. The uncontrolled distribution of adhesive also increases the possibility of leaving voids in the seal. Aside from problems controlling the adhesive, the adhesive itself may hold moisture which can escape into the housing after packaging and thereby cause the humidity level inside the housing to rise, perhaps to the detriment of the optical component.
Given these difficulties, the applicants have developed an approach for controlling the application of adhesive to the optical package 20 by partitioning the tube 22, preferably with a washer 24, to separate the adhesive 23 from the optical component 21 as shown in FIG. 2. In manufacturing an optical package 20 according to this approach, the tube 22 is held vertically and a washer 24 is placed against a ridge 25 on the inside of the tube 22. Next, the adhesive 23 is applied to the partition formed by the washer 24 and tube 22, and cured. The assembly 20 is then flipped so that the other end is up, and the procedure is repeated.
This approach offers a number of advantages over the prior art approach. First, the sealant partition confines the adhesive and prevents it from flowing into or otherwise interfering with the optical component. Furthermore, since the adhesive is applied to the washer when the tube is vertical and unobstructed with an end cap, it is easy to control the placement and volume of the adhesive. Consequently, the adhesive can be directed precisely to fill around the fiber, minimizing the risk of leaving voids which might transmit moisture. Furthermore, unlike the prior art approach, no skill is required to fill the adhesive into the end cap region and minimal fixturing is required.
The partition also facilitates “pre-sealing.” In pre-sealing, the gaps around the partition are filled with a quick-cure adhesive which cures before it has a chance to flow into the main compartment housing the optical component and potentially interfere with the optical component. Once the gaps are filled, more liberal quantities of an additional adhesive may be applied to properly seal the housing. The cure time and dispersion of the additional adhesive are not critical since there is no risk of it entering the main compartment and interfering with the optical component. Thus, the additional adhesive may be selected based on more desirable properties such as resistance to water or other ambient conditions.
Unfortunately, this approach leaves a great deal of adhesive exposed to the environment. Exposing adhesives to a moist environment is generally undesirable because moisture tends to permeate the adhesive over time and eventually enter the main compartment where it can damage the sensitive optical component. Furthermore, it is likely that the adhesive will undergo some degradation due to either ambient moisture or other ambient condition (e.g., ultraviolet radiation, abrasion, caustic substances, etc.).
In light of this shortcoming, the applicants have developed yet another approach which eliminates the adhesive's exposure to the environment. More specifically, with respect to FIG. 3, rather than just partitioning the adhesive from the optical component, the housing 31 defines a separate sealant compartment 33 which is isolated from both the optical component 31 and the environment. In manufacturing this package, a tube 32 is held vertically and a washer 38 is placed against a ridge 39 on the inside of the tube 32. An ultraviolet (UV)-curing adhesive 34 is used to seal the edge of the washer and around the fiber 36. Next, an additional adhesive 37 is applied on top of the washer and around the end cap 35, and the end cap 35 is put in place and cured. It is expected that adhesive flows out of the end cap around its perimeter and along the fiber. The UV adhesive, however, keeps the adhesive from flowing into the compartment containing the optical component 31. Note that the end cap 35 should have the correct fit around its perimeter and through the fiber hole such that adhesive will flow through. Adhesive in these locations provides a longer path through which moisture must diffuse. Once the adhesive is cured, the device is then flipped so that the other end is presented up, and the procedure is repeated.
Pre-sealing the washer offers a number of advantages aside from keeping the end cap adhesive from entering the chamber as mentioned above. Specifically, if the washer is not pre-sealed, it is necessary to use an adhesive of a certain viscosity which is thick enough not to flow through the hole in the washer, but which is thin enough to flow around all components that are to be bonded. The choice of adhesive is complicated by the fact that adhesives tend to flow more easily when they are heated which is often required for curing epoxies. Furthermore, when the tube is sealed, air is trapped inside the tube. If the tube is heated or cooled before the end cap adhesive has cured, the pressure inside the tube changes, forcing air out of or into the tube through the uncured adhesive. This can result in a permanent leak path once the end cap adhesive has cured. Pre-sealing avoids these complications. Pre-sealing also protects the internal components from any vapor which might be released during the cure of the end cap adhesive. The features of pre-sealing allow a wider variety of adhesives to be used for the final end cap sealing.
The advent of the sealant compartment offers a number of significant advantages. In addition to the advantages of the partition approach mentioned above, the sealant compartment approach also minimizes the area of adhesive that is exposed to the environment. As mentioned above this is important since moisture typically passes through adhesives over time and tends to degrade the adhesive.
Despite these advantages, however, under extreme moisture conditions, the risk remains that the adhesive barrier will be breached and moisture will enter the tube. Therefore, if the optical component contained in the tube is particularly susceptible to moisture and the environment is particularly moist, this approach may be insufficient.
Therefore, a need remains for a packaging approach that provides a high level of moisture protection for moisture-sensitive optical components, even at extreme conditions. The present invention fulfills this need among others.